We began applying diatomaceous earth to our Coryanthes at the height of the slug and bush snail season. Bush snails are tiny. Dozens can hide in the crevices between pseudobulbs. A good way to monitor slug and snail populations is to check the exterior of the raft an hour after watering. Before treatment, I found at least one slug and 10 to 50 bush snails on each wooden raft. We applied diatomaceous earth weekly throughout the spring and summer to the exposed roots, in between the pseudobulbs and to the leaves.
This summer, after renewed applications, there are 0 to 2 bush snails per plant and no sign of chewing damage to root tips or leaves from slugs or cockroaches. We plant to continue applications through the autumn.
- Look for "Food Grade Diatomaceous Earth" in order to get freshwater diatoms. Avoid "Pool Grade," which is saltwater-derived.
- Keep the package sealed and out of the greenhouse or any other humid environment. The powder is highly porous and once it absorbs water from the atmosphere, it loses its ability to dehydrate pests.
- Wear a dust mask. Silica dust is harmful to lung tissue.
- Apply diatomaceous earth once a week to the entire plant and its mount when the surfaces are dry: the new shoots, leaves, flower spikes, the slab and in between pseudobulbs. Let it sit at least overnight before you water again, since water will wash it away.
- Any soft brush will work as an applicator, but I like the idea of battling an enemy with a cosmetic brush. Drugstores carry them.